38 Concrete in Australia Vol 40 No 2
FEATURE: FIBRE REINFORCED POLYMER
100 mm to 152 mm and the height varied from 152 mm to
762 mm, with the majority of the specimens having a 152
mm diameter and 305 mm height. The average compressive
strength of the concrete ranged from 35 to 120 MPa with
all batches of concrete mixed and cured at The University of
Adelaide.
The majority of the CFFT specimens were prepared
using a manual wet lay-up process by wrapping epoxy resin
impregnated fibre sheets around precision cut styrofoam
templates. Only the specimens with fibres oriented at an
inclined angle were selected to be manufactured using an
automated filament winding process, which was performed
at the University of Alberta in Canada. Specimens not
manufactured as CFFTs were prepared as FRP-wrapped
specimens, where a thin layer of epoxy resin was applied to the
concrete surface prior to manually wrapping the fibre sheets
around precast concrete cylinders. All CFFTs and FRP-wrapped
specimens constructed using the manual wet lay-up technique
had fibre sheets oriented in the hoop direction with at least 100
mm overlap unless otherwise indicated. The CFFT specimens
manufactured by an automated filament winding process had
fibre winding angles of 45, 60, 75 and 88 degrees relative to the
longitudinal axis to examine the influence of fibre orientation.
The type of fibre used in this experimental program included
aramid and carbon FRP (AFRP and CFRP), with examples of
these fibres shown in Figure 1. The epoxy adhesive consisted of
two parts, epoxy resin binder and thixotropic epoxy adhesive,
which were mixed at a ratio of 3:1. FRP coupons, with 25 mm
width and a clear span of 138 mm length, were manufactured
and tested in parallel to the FRP-confined concrete specimens
in accordance with ASTM standard D3039M-08 (ASTM,
2008). Examples of the manufacturing methods of the FRP-
confined concrete specimens are shown in Figure 2. The
manufacturer-supplied material properties of the unidirectional
fibre sheets and the fibres used in the manufacture of the
filament wound tubes are shown in Table 1, together with the
properties determined from coupon tests.
The specimens were prepared using two different grades
of concrete, namely NSC and HSC. In this paper, unconfined
concrete strength (f’
co
) below 55 MPa is referred to as NSC and
over 55 MPa as HSC. In designing the FRP confinement, due
consideration was given to the well understood influence of the
strength of concrete on its confinement demand (Ozbakkaloglu
2013c; Ozbakkaloglu & Vincent, 2013). This was done by
selecting the number of FRP layers dependent on concrete
strength with higher strength concrete specimens receiving
proportionally more layers to ensure adequate confinement.
Provided by manufacturer
Obtained from coupon tests
Type
Nominal
fibre
thickness
(mm)
Ultimate
tensile
stress
(MPa)
Ultimate
tensile
strain
(%)
Elastic
modulus
(GPa)
Ultimate
tensile
stress
(MPa)
Ultimate
tensile
strain
(%)
Elastic
modulus
(GPa)
Aramid sheet type 1
0.2 or 0.3
2600
2.2
118.2
2390
1.86
128.5
Aramid sheet type 2
0.2
2900
2.5
120
2663
2.12
125.7
Aramid filament used in
wound tubes
2930
2.9
99
Carbon
0.117
3800
1.55
240
3626
1.44
251
Table 1: Material properties of fibres.
(a)
(b)
(c)
(d)
Figure 1: Materials for manufacturing FRP-confined specimens: (a) unidirectional aramid fibre sheet; (b) unidirectional carbon fibre sheet; (c) mixing epoxy
resin; (d) preparing epoxy resin for application.
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